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Synlett 2012; 23(7): 1021-1024
DOI: 10.1055/s-0031-1290527
DOI: 10.1055/s-0031-1290527
letter
Enantiospecific First Total Synthesis of ent-Allothapsenol
Further Information
Publication History
Received: 15 January 2012
Accepted after revision: 14 February 2012
Publication Date:
29 March 2012 (online)
Dedicated to Professor A. J. Rao on the occasion of his 70th birthday
Abstract
The enantiospecific first total synthesis of the enantiomer of the irregular sesquiterpene from Ligusticumgrayi allothapsenol, starting from the readily available monoterpene (R)-carvone, is described, which confirmed the assumed absolute configuration of the natural product.
Supporting Information
- for this article is available online at http://www.thieme-connect.com/ejournals/toc/synlett.
- Supporting Information
-
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- 6 Yields refer to isolated and chromatographically pure compounds. All the compounds exhibited spectral data [IR, HRMS, 1H NMR (400 MHz) and 13C NMR (100 MHz)] consistent with their structures. Selected Spectral Data for (1R,2R,4R,6R,9S)-4-Isopropenyl-1,6,7,7-tetramethyltricyclo[4.3.0.02,9]-nonan-8-one (10): [α]D 23 +116.9 (c 3.7, CHCl3). IR (neat): νmax= 1721 (C=O), 1381, 1017, 885 cm–1. 1H NMR (400 MHz, CDCl3): δ = 4.65 (1 H, s) and 4.58 (1 H, s) [C=CH 2], 2.10–1.95 (2 H, m), 1.87 (1 H, d, J= 10.1 Hz), 1.69 (3 H, s, olefinic CH3), 1.75–1.25 (3 H, m), 1.28 (3 H, s), 1.17 (3 H, s), 1.06 (3 H, s) and 0.81 (3 H, s) [4 × t-CH3], 0.68 (1 H, td, J = 14.0, 6.4 Hz). 13C NMR (100 MHz, CDCl3): δ = 217.5 (C=O), 148.6 (C=CH2), 108.9 (C=CH2), 58.3 (C, C-7), 40.3 (C), 39.4 (CH), 38.5 (CH), 38.1 (CH2), 30.1 (CH), 28.9 (C), 26.3 (CH3), 24.7 (CH2), 24.1 (CH3), 21.3 (CH3), 19.9 (CH3), 18.6 (CH3). HRMS: m/z calcd for C16H24O [M + Na]: 255.1725; found: 255.1726.(1R,6S)-1,6,9,9-Tetramethylbicyclo[4.3.0]non-4-ene-3,8-dione (3): [α]D 23 –35.5 (c 2.4, CHCl3). IR (neat): νmax = 1737 (C=O), 1683 (C=O), 1458, 1390, 1379, 1267, 1117, 1087, 785 cm–1. 1H NMR (400 MHz, CDCl3 + CCl4): δ = 6.66 (1 H, d, J = 10.1 Hz, H-5), 5.98 (1 H, d, J = 10.1 Hz, H-4), 2.63 (1 H, d, J = 19.2 Hz), 2.47 (1 H, d, J = 16.4 Hz), 2.46 (1 H, d, J = 19.2 Hz), 2.29 (1 H, d, J = 16.4 Hz), 1.34 (3 H, s), 1.10 (3 H, s), 1.06 (3 H, s), 1.01 (3 H, s) [4 × t-CH3]. 13C NMR (100 MHz, CDCl3 + CCl4): δ = 219.9 (C, C-8), 198.8 (C, C-3), 156.8 (CH, C-5), 126.5 (CH, C-4), 53.3 (C), 48.6 (CH2), 47.8 (C), 45.0 (CH2), 41.1 (C), 25.3 (CH3), 22.8 (CH3), 22.6 (CH3), 19.5 (CH3). HRMS: m/z calcd for C13H18O2 [M + Na]: 229.1204; found: 229.1206. (1R,2R,3S,6R)-3-Hydroxy-1,2,6,9,9-pentamethylbicyclo-[4.3.0]nonan-8-one (21): [α]D 22 –54.4 (c 4.0, CHCl3). IR (neat): νmax = 3510 (OH), 1719 (C=O), 1381, 1246, 1227, 963 cm–1. 1H NMR (400 MHz, CDCl3): δ = 3.84 (1 H, br s, CHOH), 2.66 (1 H, d, J = 17.6 Hz, H-7A), 1.95 (1 H, ddd, J = 14.2, 9.3, 7.5 Hz), 1.86 (1 H, d J = 17.6 Hz, H-7B), 1.74–1.68 (2 H, m), 1.60 (1 H, br s), 1.33–1.28 (1 H, m), 1.10–1.05 (15 H, m, 4 × t-CH3 and s-CH3). 13C NMR (100 MHz, CDCl3): δ = 224.4 (C, C=O), 72.0 (CH, C-3), 54.1 (C), 48.3 (C), 47.9 (CH2), 40.1 (C), 38.1 (CH), 29.2 (CH2), 28.4 (CH2), 28.1 (CH3), 26.1 (CH3), 25.9 (CH3), 15.9 (CH3), 15.2 (CH3). HRMS: m/z calcd for C14H24O2Na [M + Na]: 247.1674; found: 247.1672.(1R,6R)-1,2,6,9,9-Pentamethyl-8-methylenebicyclo-[4.3.0]non-2-ene [Allothapsa-2,8(12)-diene (19)]: [α]D 22 –11.5 (c 1.1, CHCl3). IR (neat): νmax = 3069, 1648, 1377, 1075, 879 cm–1. 1H NMR (400 MHz, CDCl3): δ = 5.40 (1 H, br s, H-3), 4.84 (1 H, d, J= 2.2. Hz) and 4.79 (1 H, d, J = 2.3 Hz), 2.57 (1 H, dt, J = 15.6, 2.2 Hz) and 2.04 (1 H, d, J = 15.6 Hz) [H-7], 2.15–1.98 (1 H, m), 1.95–1.80 (1 H, m), 1.80–1.65 (1 H, m), 1.66 (3 H, s, vinylic CH3), 1.15–1.00 (1 H, m), 1.12 (3 H, s), 1.11 (3 H, s), 0.99 (3 H, s) and 0.90 (3 H, s) [4 × t-CH3]. 13C NMR (100 MHz, CDCl3): δ = 162.9 (C, C-8), 137.1 (C, C-2), 121.7 (CH, C-3), 104.6 (CH2, C=CH2), 51.4 (C, C-1), 47.2 (CH2), 46.7 (C), 41.2 (C), 32.3 (CH2), 31.5 (CH3), 30.3 (CH3), 22.1 (2 C, CH3 and CH2), 21.5 (CH3), 19.2 (CH3). MS: m/z (%) = 204 (100) [M+], 189 (12), 166 (22), 135 (18), 121 (100).(1R,6R,8S)-1,2,6,9,9-Pentamethylbicyclo[4.3.0]nona-2-ene-8-methanol [8-Epiallothapsenol (20)]: [α]D 22 –5.4 (c 0.4, CHCl3). IR (neat): νmax = 3338 (OH), 1545, 1377, 1083, 1067, 1018, 818, 669 cm–1. 1H NMR (400 MHz, C6D6): δ = 5.46 (1 H, br s, olefinic H), 3.51 (1 H, dd, J = 10.2, 5.8 Hz), 3.23 (1 H, dd, J= 10.2, 7.9 Hz), 2.13–1.76 (2 H, m), 1.74–1.68 (2 H, m), 1.67 (3 H, s, vinylic CH3), 1.33–1.30 (2 H, m), 1.23 (1 H, dd, J= 13.3, 9.8 Hz), 1.06 (3 H, s), 0.93 (3 H, s) 0.90 (3 H, s), 0.86 (3 H, s) [4 × t-CH3]. 13C NMR (100 MHz, C6D6): δ = 138.7 (C, C-2), 124.2 (CH, C-3), 64.9 (CH2, CH2OH), 53.6 (C), 49.2 (CH), 46.2 (C), 44.9 (CH2), 42.0 (C), 38.9 (CH2), 28.4 (CH3), 25.9 (CH3), 23.2 (CH2), 22.7 (CH3), 21.8 (CH3), 20.4 (CH3).(1R,6R,8R)-1,2,6,9,9-Pentamethylbicyclo[4.3.0]nona-2-ene-8-methanol [ent-Allothapsenol (ent-1)]: [α]D 22 –28.5 (c 0.3, CHCl3). IR (neat): νmax = 3342 (OH), 1376, 1074, 1017, 817 cm–1. 1H NMR (400 MHz, C6D6): δ = 5.42 (1 H, br s, olefinic H), 3.45 (1 H, dd, J = 10.4, 7.0 Hz), 3.26 (1 H, dd, J = 10.3, 6.7 Hz), 2.10–1.75 (4 H, m), 1.61 (3 H, s, vinylic CH3), 1.40 (1 H, br s), 1.35 (1 H, dd, J = 12.5, 5.3 Hz), 1.25 (1 H, t, J = 12.7 Hz), 1.12 (3 H, s), 0.96 (3 H, s), 0.86 (3 H, s), 0.85 (3 H, s) [4 × t-CH3]. 13C NMR (100 MHz, C6D6): δ = 137.7 (C, C-2), 122.2 (CH, C-3), 64.6 (CH2, CH2OH), 52.5 (C), 50.7 (CH), 44.2 (C), 42.8 (CH2), 42.5 (C), 33.6 (CH3), 32.9 (CH2), 23.5 (CH3), 23.3 (CH3), 22.7 (CH2), 21.7 (CH3), 20.1 (CH3)
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